1. Field of the Invention
The present invention relates to a cable clamp and more particularly to a wedge-operated cable clamp for clamping an object to a running cable or alternatively for clamping a traveling carriage or other object to a fixed cable.
2. Description of the Prior Art
One method of logging involves the use of a so-called "skyline carriage" moving along a fixed, suspended skyline cable to skid or carry logs from the woods to a log collection point or "landing". There the logs are loaded onto trucks and transported to a lumber or plywood mill for processing. The skyline carriage is equipped with a cable clamp to hold the carriage in a desired position on its skyline when not traveling along it, such as when logs are being attached to the carriage in the woods or unloaded from the carriage at the landing.
Known cable clamps, including those for skyline carriages, apply a clamping force to the cable which is directly porportional to an external primary force applied to the clamping members by a power device such as a fluid cylinder. If the primary force generated by the power device is insufficient to prevent slippage of the clamp and cable relative to one another because of the load on the carriage or other traveling object mounting the clamp in the case of a fixed line, or because of the tension on the running cable where the clamp is mounted on a stationary object, the slippage cannot be arrested. In the case of skyline carriages, slippage of the cable clamp makes loading and unloading operations difficult and endangers the lives of persons working below the carriage.
Cable clamps for skyline carriages representative of the prior art are shown in U.S. Pat. No. 3,863,774, 3,718,262; and 2,330,736. The cable clamps shown in these three patents all use the same basic principle; a primary force generated by a spring or cable tension applies a clamping force through a system of interconnected levers and linkages to a movable clamping member to force the movable clamping member toward a fixed clamping member to clamp a cable therebetween. Because of the system of interconnected linkages used, once a cable starts to slip between the clamping members, no greater clamping force is inherently generated. Only an increase in the applied primary force, if any increase is available, will increase the gripping force on the cable to stop the slippage.
Perhaps the closest prior art is represented by the Goepel U.S. Pat. No. 1,201,169 showing a different type of cable grip or clamp, the clamping force of which is directly proportioned to the tension in a cable or chain induced by an attached load to be carried. The clamp has a fixed clamping member on one side of the cable and a wedge-shaped movable clamping member on the opposite side of the cable which slides along an inclined plane to apply a clamping force to the cable. The movable clamping member is slid into gripping contact with the cable by a lever connected directly to the load cable so that the gripping force of the clamp depends directly on the tension on the load cable. Although there would be some tendency for the wedge-shaped clamping member to apply a progressive wedging force to the cable should it start to slip, such tendency occurs in only one direction of slippage and is inhibited by the tension in the load cable itself because of the direct connection between the load cable and the clamping member.
Accordingly, there is a need for an improved cable clamp which will automatically apply an increased clamping force to the cable upon increases in the tendency of the clamp and cable to slip relative to one another.
SUMMARY OF THE INVENTION
The present invention is an improved cable clamp suitable for use in clamping a movable object such as a skyline carriage to a fixed cable or alternatively for clamping any object to a running cable.
A primary feature of the cable clamp of the invention is its ability to self-energize to apply a progressively increasing clamping force to a cable automatically upon increases in forces tending to cause slippage between the cable and the clamp.
Another important feature is the ability of the clamp to self-energize to prevent slippage of the clamp in either of opposite directions along the cable.
Another primary feature is the ability of the clamp to apply its self-energizing progressive clamping force without any increase in the primary clamp-activating force.
Another feature of the clamp is its use of a series of interrelated wedging surfaces to generate the aforementioned self-energizing progressive clamping force.
Still another feature of the invention is the use of a series of interrelated but disconnected and independently movable clamping members embodying the aforementioned wedging surfaces to enable activation and application of the self-energizing progressive clamping force independently of the primary clamp-activating force.
Primary objects of the invention are to provide a cable clamp which has the foregoing features and which is simple and foolproof in operation, easy to manufacture, and easy to activate through the application of a relatively small primary activating force as applied, for example, by a small double-acting fluid cylinder.
In a preferred embodiment, a cable clamp embodying the foregoing objects and features includes a heavy rigid box-like housing for the clamping mechanism with fixed upright sidewalls between which the movable portions of the clamping mechanism are mounted. The cable extends through the housing between the sidewalls in a cable passage between a pair of opposed laterally and longitudinally movable inner clamping members operable to clamp the cable therebetween. Each inner member is backed by an outer laterally movable member. The mating faces of the inner and outer members are longitudinally double tapered so as to be complementary to one another and to provide a wedge-clamping effect upon movement of the inner members longitudinally in either direction relative to the outer members.
The outer face of each outer member is vertically tapered and spaced from a vertical inner face of the adjacent fixed housing sidewall to provide a wedging space therebetween. Clamp-activating wedge plates with vertically tapered wedging surfaces complementary to the tapered vertical surfaces of the outer members are movable vertically within the wedging spaces in sliding engagement with the outer members and fixed sidewalls. When driven into the wedging spaces, the activating wedges generate a clamp-activating force which shifts the outer and inner members laterally toward the cable to cause the inner members to grip the cable. When the cable is gripped, any tendency of the cable and clamp to move longitudinally relative to one another shifts the inner members longitudinally relative to the outer members over their mating double-tapered faces, generating a progressive clamping force which increases with increases in the tendency of the cable and clamp to slip.
The activating wedges are moved in opposite directions within the wedging spaces by a double-acting fluid cylinder through a mechanical linkage system. Spring-operated means withdraw the inner members from engagement with the cable and return such members longitudinally to their centered or neutral positions within the housing upon withdrawl of the activating wedges from their wedging spaces.
The foregoing objects, features and advantages of the present invention will become more apparent from the following detailed description which proceeds with reference to the accompanying drawings.